Haptics refer to a technology about tactile sensation and, more particularly, to a technology for allowing a user of an electronic device to feel touch, forces, motion, etc. through a keyboard, a mouse, a joystick, a touchscreen, or the like. Although visual information accounted for most of the information exchanges between electronic devices and people in the past, the haptic technology currently attracts attention with regard to providing more detailed and realistic information.
In general, an inertial actuator, a piezoelectric actuator, an electroactive polymer (EAP) actuator, an electrostatic actuator, etc. are used for the haptic technology. Examples of the inertial actuator include an eccentric motor that vibrates by an eccentric force generated by the rotation of the motor, and a linear resonant actuator (LRA) that maximizes the vibrational intensity by resonant frequencies. The piezoelectric actuator is in the shape of a beam or a disk and is driven by a piezoelectric element whose size or shape changes instantaneously in response to an electric field. The EAP actuator generates vibration by repeated movements of a mass attached to an EAP film. The electrostatic actuator is driven by an attractive force generated between two oppositely charged glass sheets and a repulsive force generated when the glass sheets have charges with the same polarity.
Korean Patent Publication No. 10-2011-0118584 (entitled “Transparent composite piezoelectric combined touch sensor and haptic actuator”) discloses conventional haptic devices, and FIG. 1 is a perspective view of a conventional haptic device.
In the haptic device, a layer configured to serve as a sensor and a layer configured to serve as an actuator may be combined into a single module in the form of a composite piezoelectric actuator/sensor cell. Here, FIG. 1 illustrates the cross section of a composite piezoelectric actuator/sensor cell 5 together with associated electrodes 6. The composite piezoelectric cell 5 includes an array of piezoceramic fibers 7a in a structural adhesive 7b such as an epoxy material. Each of the electrodes 6 may be used to send an individual control signal so that each patch of the fibers 7a inserted into the structural adhesive 7b between two consecutive electrodes 6 and 6 can be actuated, thereby exerting a localized haptic effect at the corresponding location. Arrows 8 indicate how the polarized piezoceramic material expands or contracts in response to an applied electric field, and arrow 9 indicates the piezoceramic polarization produced by the electrodes 6.
However, the above-described conventional haptic technology is merely used to provide simple vibration, and therefore has limitations for providing emotional tactile sensation or complicated text information. Accordingly, research needs to be conducted on a tactile supply structure capable of effectively providing emotion and complicated information as well as simply providing vibration.